Recently, it has been reported that 35% of people in cities are overweight due to increased fast food intake and lack of exercise. This phenomenon is spreading all over the world and has become a primary cause of cancers and adult diseases.
More over, the National Obesity Forum in British reported that 80% of diabetes cases, 50% of high blood pressure cases, and 25% of cancers associated with obesity would be reduced if obesity were eliminated the world. That is, obesity is become recognized as a serious problem for modern societies.
In order to solve this obesity problem, diets and eating habits must be changed and regular exercise is necessary. However, modern people have little time to do regular exercise, and it takes a long time to do aerobic exercise to get rid of obesity.
In order to solve this problem, developed are a variety of functional shoes that provide exercise effects to a user when the user simply walks, wearing the shoes without particularly devoting and or setting aside time.
As shown in FIG. 1, there are two types of conventional functional shoes. In FIG. 1, (a) is a ball-support- type shoe and (b) is an unstable ball-support-type shoe.
In the ball-support-type shoe, a sole comprises a rear portion which is low and a front portion which is high and flat. In the conventional ball-support-type shoe, a wearer's toe and ball are elevated relative to the heel when the shoe is worn by the wearer. Accordingly, the wearer will tend to stand with the body inclined slightly forward so as to maintain balance.
FIG. 2 illustrates contraction and relaxation states of muscles when the ball- support-type shoe is put on. Referring to FIG. 2, muscles of the shin and front muscles of the thigh are contracted and a scapular muscle is severely contracted.
The ball-support-type shoe has the following disadvantages. First, if a wearer wears the ball-support-type shoe for a long time, since the shin muscles, the front thigh muscles, and the scapular muscles are continuously contracted, lower body muscles are strengthened, but abdominal obesity which is the primary cause of adult disease, is not eliminated.
Second, since the trunk of a wearer is inclined forward and. thereby the scapular muscle is continuously taut, gastrointestinal disorders are caused.
Third, if the walker walks wearing the ball-support-type shoes, since the wearer walks with elevated heels giving strength to the toes, the wearer feels uneasy. Further, obese walkers and old-aged walkers may easily fall down.
Fourth, since walking strides of the wearer are not natural, the wearer is not willing to wear these shoes because of their conspicuous appearance. Accordingly, the shoes do not give good exercise effects to the wearer of the shoes.
On the other hand, the unstable ball-support-type shoe causes a walker to stand more stably compared to the ball-type-support shoe, but the walker still feels uneasy while walking with the shoes and standing inclined forwards. Accordingly, the unstable ball-support-type shoe has the same disadvantages as the ball-support-type shoe.